1. Field of the Invention
The present invention relates to manufacture of membrane test probes used in testing of integrated circuit chips, and more particularly concerns a method for tensioning the membrane of a test probe.
2. Description of Related Art
Testing of an integrated circuit chip generally involves application of various test signals to the chip and observation of resulting signals produced by the chip. Such testing is often performed before the chip is assembled into its final circuit configuration, and even while the chip is still on a wafer bearing a number of chips that have yet to be severed from one another. Various types of probe arrangements have been devised to enable electrical connection between test circuitry of a test fixture and the chip contact pads. One such probe arrangement which exhibits a number of significant advantages comprises a membrane test probe wherein a thin flexible membrane is stretched across the central opening of a rigid-flex substrate. A number of test contacts are formed on one surface of the central portion of the membrane and project outwardly therefrom. These test contacts are connected by circuit traces on the surface of the membrane to peripheral portions of the membrane and thence to test circuitry. The membrane test probe is placed adjacent the chip to be tested with its projecting test contacts in registration with contact pads of a chip to be tested. Pressure is applied to the remote face of the membrane so as to effectively push the membrane outwardly toward the chip and force its test contacts against the chip contacts. A membrane test probe of this type is shown in U.S. Pat. No. 5,264,787 for RIGID-FLEX CIRCUITS WITH RAISED FEATURES AS IC TEST PROBES by Blake F. Woith, William R. Crumly and Jacques F. Linder, and U.S. Pat. No. 5,148,103 for APPARATUS FOR TESTING INTEGRATED CIRCUITS, by J. Pasiecznik. Both of these patents are assigned to the assignee of the present invention.
When the test membrane is pressed against the integrated circuit chip, the testing pressure exerted on the membrane may cause the membrane to be distorted and effectively to exhibit a drape wherein parts of the very thin flexible membrane tend to bend over and around contact pads of the chip. This drape creates undesirable stresses on the thin circuit traces and may possibly cause undesired contact between membrane circuit traces and the chip surface. Excessive drape may tend to misalign test probe contacts and chip contacts. To minimize this drape, it has been suggested to provide different types of pressure backup blocks at the back of the membrane, some with particular surface configurations. Axial pressure is provided behind the membrane by means of a backup plate or pressurized gas, so as to distend the membrane and create radial tension therein during testing that would tend to overcome such a drape. The use of such devices for overcoming drape during conduct of a test procedure is difficult, adds to the complexity of the arrangement and is unreliable. Precise repeatability of the test conditions becomes difficult to obtain. Yet there is still insufficient assurance that the undesired drape of a membrane is uniformly eliminated.
Accordingly, it is an object of the present invention to provide a test probe membrane that avoids or minimizes the above-mentioned problems.